Is it permissible for a worshiper, while reciting Allah's words, "Guide us to the straight path – the path of those upon whom You have bestowed favor," to bring to mind specific righteous individuals?

It is a religious requirement for the worshipper to ponder on what they recite, as this is the very purpose of recitation. They should discern and understand from each verse what is appropriate to it. There is no harm, when pondering on the verses, in recalling the biographies of the righteous, and asking God for guidance to be like them. It is more preferable to recall the biographies of the early Muslims (Salaf). "Those upon whom You have bestowed favor" are the angels, prophets, the truthful, martyrs, and the righteous, among whom are the Messenger (peace be upon him), Abu Bakr, and Umar. It is important to note that one should not get carried away with pondering during prayer, especially if praying behind an Imam, so as not to distract them from following the Imam or cause them to miss understanding what they are reciting.